Resin for composite structures

ABSTRACT

A resin precursor composition for use in the production of composite components includes an isocyanate component comprising a material selected from the group consisting of diphenylmethane diisocyanate, a polymeric isomer of diphenylmethane diisocyanate, and combinations thereof. The resin precursor composition also includes at least one polyether polyol having a functionality of three in an amount such that the ratio of the isocyanate component to the at least one polyol is between approximately 80% and 115% of stoichiometric. The resin precursor composition also includes a mold release material and a filler material.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present invention is related to U.S. patent application Ser. No.11/287,140 titled “Method for Producing Pultruded Components”; U.S.patent application Ser. No. 11/287,143 titled “System for ProducingPultruded Components”; and U.S. patent application Ser. No. 11/287,142titled “Pultruded Component”, each of which were filed on the same dateas the present application.

BACKGROUND

The present invention relates generally to methods and systems forproducing fiber reinforced composite components using a pultrusionprocess. More specifically, the present invention relates to compositecomponents that utilize a polyurethane resin matrix.

Fiber-reinforced composite structural components that are formed in apultrusion process typically include a fibrous reinforcing material(e.g., glass, polymeric, or carbon fibers) embedded in a resin matrix(e.g., a polymer such as an unsaturated polyester or epoxy vinyl ester).The fibrous reinforcing material typically includes both yarns or tows(each of which include a large number of fibers or filaments) and one ormore mats or webs of fibers.

To produce composite structural components such as lineals for use inwindows and doors, the tows are coated by pulling them through anatmospheric pressure bath (typically an open vat or tub) of liquid resinprecursor material. Once coated, the tows are pulled through a curingdie to polymerize and set the resin. One difficulty with usingatmospheric pressure baths to coat the tows is that the individualfibers or filaments within the tows may not be adequately coated withresin. For example, the outer surface of the tows may be coated withresin, while the filaments or fibers on the inside of the tows may beonly partially coated.

Because the strength of the composite structural component is largelydependent upon the interaction between the resin matrix and the fibrousreinforcement, it is desirable to completely coat as many of theindividual filaments or fibers as possible. Uncoated filaments are notstructurally supported, and are unable to take any significantcompressive load. In addition, void areas intermingled with thefilaments become sites where cracks will initiate under load, therebyreducing both the stiffness and the strength of the composite component.Thus, it would be advantageous to reduce the number of partially coatedfilaments, voids, or the like that are present in the finishedcomponent.

Another difficulty associated with atmospheric pressure baths is thatthey generally contain a relatively large volume of uncured resinprecursor chemicals, and a large surface area of these chemicals isexposed to the atmosphere. Vaporization of such chemicals into thesurrounding atmosphere may be undesirable, and mitigation systemsdesigned to reduce the vapor emissions may be relatively costly and mayimpede many of the tasks required to maintain product quality andproductivity.

Conventional resins used in the production of pultruded compositecomponents (e.g., polyesters, vinyl esters, phonolics, etc.) have anultimate strength of between approximately 8,000 and 15,000 psi, and anelastic modulus between approximately 350,000 and 500,000 psi. Thiselastic modulus is well matched to that of the reinforcing fibers. Whena compression or bending load is applied to such a composite component,the load is shared among the reinforcing fibers in a manner that resultsin relatively balanced loading and relatively high ultimate strength.However, the elongation-to-failure of these conventional resin systemsis typically between approximately 1.5% and 3%, and is exceeded beforethat of the fibers, which may have an elongation-to-failure of 4% to 6%.The resin will fracture when its elongation-to-failure is exceeded,leaving the fibers unsupported. This allows the load to concentrate in asmall percentage of the available fibers, exceeding their ultimatestrength and resulting in the failure of the component at loads that arebelow the theoretical maximum of the complete fiber reinforcementpackage.

Conventional resins used in the production of pultruded compositecomponents also have relatively little strength in the directiontransverse to the longitudinal (i.e., pulling) direction. As a result,pultruded composite components may utilize reinforcing fibers orientedin the transverse orientation to provide the necessary transversestrength for the component. For example, the reinforcing material mayinclude both fiber tows that extend through the pultruded component inthe longitudinal direction and fiber mats that provide multidirectionalstrength for the component. However, the inclusion of transverse fibersor fiber mats undesirably adds weight and cost to the component and alsoadds processing difficulties to the production of the component.

Accordingly, there is a need to provide an improved resin system toprovide enhanced structural strength for pultruded composite componentsas compared to that provided by conventional resin systems. There isalso a need for a composite component that does not utilize transversereinforcing fibers but that has sufficient transverse strength toprovide resistance to bending and to allow the component to be securedwith screws, nails, or the like. There is further a need to provide animproved system and method for coating reinforcing materials with apolymeric material in a pultrusion process.

SUMMARY

An exemplary embodiment of the invention relates to a resin precursorcomposition for use in the production of composite components thatincludes an isocyanate component comprising a material selected from thegroup consisting of diphenylmethane diisocyanate, a polymeric isomer ofdiphenylmethane diisocyanate, and combinations thereof. The resinprecursor composition also includes at least one polyether polyol havinga functionality of three in an amount such that the ratio of theisocyanate component to the at least one polyol is between approximately80% and 115% of stoichiometric. The resin precursor composition alsoincludes a mold release material and a filler material.

An exemplary embodiment of the invention relates to a polyurethane resinprecursor composition for use in a pultrusion process that includes anisocyanate material comprising a material selected from the groupconsisting of diphenylmethane diisocyanate, a polymeric isomer ofdiphenylmethane diisocyanate, and combinations thereof. The polyurethaneresin precursor also includes a first polyether polyol having afunctionality of three and a molecular weight of between approximately600 and 800, a second polyether polyol having a functionality of atleast three and a molecular weight of between approximately 100 and 300,a mold release material, and a filler material.

An exemplary embodiment of the invention relates a method for producinga resin precursor composition that includes mixing at least onepolyether polyol having a functionality of three with a mold releasematerial and a filler material to form a first resin precursorcomponent. The method also includes mixing a second component with thefirst component to form a resin precursor composition, the secondcomponent comprising an isocyanate comprising a material selected fromthe group consisting of diphenylmethane diisocyanate, a polymeric isomerof diphenylmethane diisocyanate, and combinations thereof. The step ofmixing the second component with the first component is performed lessthan approximately five minutes before the resin precursor compositionis to be provided to an impregnation die of a pultrusion process.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a generic composite component producedin a prior art pultrusion process.

FIG. 2 is a perspective view of a generic composite component producedin a pultrusion process according to an exemplary embodiment thatutilizes an improved resin to eliminate the need for transverse fiberreinforcement.

FIG. 3 is a schematic view illustrating components of a pultrusion lineaccording to an exemplary embodiment.

FIG. 4 is a perspective view of an impregnation die for use in producinga composite component according to an exemplary embodiment.

FIG. 5 is an exploded perspective view of the impregnation dieillustrated in FIG. 4.

FIG. 6 is a cross-sectional view of the impregnation die illustrated inFIG. 4.

FIG. 7 is a flow diagram illustrating steps in a method of producing acomposite component according to an exemplary embodiment.

DETAILED DESCRIPTION

According to an exemplary embodiment, a method and apparatus areprovided for producing a pultruded composite component using an improvedresin system. The composite components are provided in the form oflineals or other components for use in the production of windows, doors,and the like. According to other exemplary embodiments, any of a varietyof other composite components may be produced using the resin, system,and methods described herein, including handles for brooms, shovels, andother hand tools; sheet pilings for erosion protection; frame membersand door reinforcements for trucks and automobiles; structural elementsfor water cooling towers and RF-transparent structures such as cellulartelephone towers; concrete reinforcing bars; highway delineators, guardrailings, and posts; non-conductive and corrosion-resistant grating foroil drilling platforms and chemical plants; and any of a variety ofother products.

The improved resin system is intended to provide the compositecomponents with relatively high bending and compressive strength suchthat the components may be produced without the need to provide fiberreinforcement in the transverse direction (i.e., the directionperpendicular to the longitudinal or “pulling” direction). Suchcomponents may advantageously be produced at a lower weight, materialcost, and capital cost as compared to conventional composite componentsusing traditional resin systems. In contrast to conventional pultrusionprocesses that utilize transverse fibers (e.g., webs or mats of fibersincorporated in the component), the production speed of the compositecomponents according to the exemplary embodiments described herein arenot slowed by the addition of the transverse fibers, thereby requiringfewer machines to supply the desired quantity in a given time frame.

FIG. 1 illustrates a conventional generic pultruded composite component10 that utilizes both fibers oriented in the longitudinal direction(shown as fibers 24 oriented in the “X” direction) and fibers orientedin the transverse direction (shown as fibers 18 oriented in the “Y”direction). The transverse fibers 18 may be provided, for example, aslayers 12, 14, and 16, which include mats of fibers that are impregnatedwith a resin precursor 26. As shown in FIG. 1, layers 20 and 22 oflongitudinally-oriented fibers (which also are impregnated with theresin precursor 26) are provided intermediate or between the mats 12,14, and 16. Because the composite component 10 shown in FIG. 1 utilizesa conventional resin system (e.g., polyester, vinyl ester, or phenolicresins, etc.), the layers 12, 14, and 16 of fibers are necessary toprovide transverse strength for the component 10.

FIG. 2 is a perspective view of a generic pultruded component 50produced using a resin system that provides enhanced structural rigidityaccording to an exemplary embodiment. As illustrated in FIG. 2, thecomponent 50 does not utilize fibers oriented in the transversedirection (i.e., the “Y” direction); instead, fibrous reinforcement isprovided such that the fibers 54 are oriented only in a direction thatis substantially parallel to the longitudinal direction (i.e., the “X”direction). The strength that was provided by the transverse fibers 18in FIG. 1 is instead provided by a resin 56 having improved mechanicalproperties as compared to conventional resin systems. The component 50may therefore be produced in a relatively simple manner that does notrequire the additional expense and difficulty associated with the use oftransverse fibers.

According to an exemplary embodiment, composite components (e.g., suchas component 50) are produced using a resin precursor that issubstantially composed of a polyurethane material having improvedmechanical characteristics in both the longitudinal and transversedirections as compared to components using conventional resin systems.Experimental data was compiled for a pultruded composite component madewith a polyurethane resin system and a pultruded composite componentmade with a conventional unsaturated polyester resin system, both ofwhich had the same glass reinforcement content. The longitudinalflexural strength of the component made with polyurethane resin was230,000 psi, nearly three times the 80,000 psi longitudinal flexuralstrength for the comparable component made with a conventional polyesterresin system. The longitudinal elongation to failure of the polyurethanecomponent was 3.2 percent, compared to 1.8 percent for the conventionalpolyester component. Results were similar in the transverse direction.The pultruded component made with a polyurethane resin exhibited atransverse flexural strength of approximately 15,100 psi, more thanthree times that of the component made with an unsaturated polyesterresin (4,800 psi). Transverse flexural elongation to failure wasslightly higher as well: 1.4 percent for the polyurethane component ascompared to 1.2 percent for the unsaturated polyester component.

The type of fibrous reinforcement utilized may differ according tovarious exemplary embodiments, and may depend on requirements for theparticular application in which the composite component will beutilized. According to an exemplary embodiment, the longitudinal fibersmay be provided as glass fibers. According to other exemplaryembodiments, the fibers may be polymeric fibers, carbon fibers, or anyother suitable fibers that may be utilized in the production ofpultruded products.

It should be noted that while FIG. 2 illustrates a component 50 having agenerally rectangular solid shape, components utilizing the resin systemand produced by the method described herein with reference to thevarious exemplary embodiments may be provided in any number of sizes,shapes, and configurations. Features may be provided in the componentsthat enable their use in various applications, including use in linealsand other structural components for windows, doors, and the like.Additionally, pultruded components may be produced using the resinformulations described herein that have fibrous reinforcement orientedboth in the longitudinal direction and in one or more other directionsthat are not substantially parallel to the longitudinal direction(including fibers that may be oriented in the transverse direction).

According to an exemplary embodiment, the polyurethane resin precursorsystem includes an isocyanate, a polyol or polyol blend, and a system oflubricants and other additives that are typically referred to as a “moldrelease.” The resin system may also optionally include one or morepolymeric additives that may be used to modify the surface of theresulting component, to modify the physical properties of the component,to provide improved processing, or to provide other benefits.Additionally, the resin system may include one or more fillers which mayact passively to reduce the cost of the overall resin system (e.g., bytaking the place of more costly constituents) or may actively functionto provide improved physical properties or improved processing.

The ratio of the isocyanate component to the polyol component isweighted according to the fraction of the components that are reactive.According to an exemplary embodiment, the ratio of isocyanate to polyolis between approximately 80% and 115% of stoichiometric. According toanother particular exemplary embodiment, the ratio of isocyanate topolyol is between approximately 90% and 110% of stoichiometric.According to a particular exemplary embodiment, the ratio of isocyanateto polyol is between approximately 95% and 105% of stoichiometric.

The mold release component of the resin precursor system is provided inan amount sufficient to prevent adhesion of the resin precursor systemto the die surface, thereby giving the part a relatively smooth surfaceand reducing the force required to move the part through the curing die.The mold release includes an acid component that is attracted to themetallic surface of the die (due to its highly polar nature) and forms alubricating layer. The acid component is soluble in the polyol mixture;but as the polyol is consumed, it precipitates out of solution and isdriven towards the surface of the gelling mass. These two forcesconcentrate the acid component of the mold release at the surface,improving its release performance compared to a substance that mighthave the same lubricity but no tendency to concentrate at the surface.Trade names of suitable mold release systems include Pul-24,commercially available from Axel Plastics, and CR-250, commerciallyavailable from Technick Products.

According to an exemplary embodiment, the mold release component isprovided at a level of between approximately 0.5% and 5% of the totalmass of the resin. According to a preferred embodiment, the mold releasecomponent is provided at a level of between approximately 0.5% and 3% ofthe resin. According to a particularly preferred embodiment, the moldrelease component is provided at a level of between approximately 0.5%and 2.5% of the resin.

The polymeric additive is provided in an amount sufficient to improvethe surface quality of the finished part by reducing the shrinkage ofthe resin as it cures so that the surface of the curing resin remains incontact with the polished die surface and retains the smoothcharacteristic of the die surface. According to an exemplary embodiment,the polymeric additive is provided at a level of between approximately0% and 25% of the total mass of the resin. According to a preferredembodiment, the polymeric additive is provided at a level of betweenapproximately 2% and 15% of the total mass of the resin. According to aparticularly preferred embodiment, the polymeric additive is provided ata level of between approximately 4% and 10% of the total mass of theresin.

The filler component of the resin precursor system is provided in anamount sufficient to increase the viscosity (and thereby the shearforce) of the resin layer between the outermost glass fibers and the diesurface, and to react with the acidic elements of the mold release toprovide a significant body of lubricative particles between theoutermost glass fibers and the die surface. The filler component mayinclude a solid such as caolin clay or calcium carbonate. The calciumcarbonate may either be untreated or may be treated with a stearic oroleaic acid to modify its surface.

According to an exemplary embodiment, the filler component may beprovided at a level of between approximately 0.5% and 20% of the totalmass of the resin. According to a preferred embodiment, the fillercomponent may be provided at a level that is substantially equal to themass percentage of the mold release component.

The isocyanate component can be any one of several low to intermediategrades of diphenylmethane diisocyanate (MDI), its polymeric isomers(pMDI), and blends thereof. The isocyanate component has an NCO(nitrogen-carbon-oxygen) or cyanate percentage of between approximately25% and 32%, preferably between approximately 27% and 31.5%, and mostpreferably between approximately 31.2% and 31.5%. The viscosity of theisocyanate component is between approximately 100 and 500 centipoise(cps), preferably between approximately 100 cps and 250 cps, and mostpreferably approximately 200 cps.

Trade names of products that may be used as isocyanate componentsaccording to various exemplary embodiments include Mondur 448, Mondur486, Mondur MR and Mondur MR (Light), which are commercially availablefrom Bayer MaterialScience; Lupranate M20S and Lupranate M20SB, whichare commercially available from BASF; Isobind 1088 and Papi 27, whichare commercially available from Dow Chemical Company; and Rubinate M,which is commercially available from Huntsman Polyurethanes.

The polyol component of the resin precursor system may consist of asingle polyol or may be provided as a blend of two or more polyols.

According to an exemplary embodiment, the polyol component is providedas a single polyol having the following characteristics: (a) the polyolhas a functionality of three, preferably with all of the hydroxyl groupsbeing primary hydroxyls (i.e., readily available to react); (b) thepolyol is a polyester or polyether polyol, preferably a polyetherpolyol; (c) the polyol has an OH index between approximately 500 and 700mgOH/g, preferably between approximately 600 and 700 mgOH/g, and mostpreferably between approximately 675 and 700 mgOH/g; (d) the polyol hasa molecular weight between approximately 200 and 300, preferably betweenapproximately 225 and 275, and most preferably approximately between 240and 250; and (e) the polyol has a viscosity below approximately 1000 cpsand preferably below 900 cps. Trade names of suitable polyols includeVoranol 230-660, which is commercially available from Dow ChemicalCompany and Multranol 9138, which is commercially available from BayerMaterialScience.

According to another exemplary embodiment, the polyol component isprovided as a blend of two polyols.

The first polyol in the two-polyol blend has the followingcharacteristics: (a) the polyol has a functionality of three, preferablywith all of the hydroxyl groups being primary hydroxyls; (b) the polyolis a polyester or polyether polyol, preferably a polyether polyol; (c)the polyol has an OH index between approximately 200 and 300 mgOH/g,preferably between approximately 230 and 250 mgOH/g, and most preferablybetween approximately 235 and 240 mgOH/g; (d) the polyol has a molecularweight between approximately 600 and 800, preferably betweenapproximately 650 and 750, and most preferably between approximately 680and 720; and (e) the polyol has a viscosity below approximately 500 cps,preferably below approximately 400 cps, and most preferably betweenapproximately 240 and 270 cps. Trade names of suitable polyols for useas the first polyol include CAPA 3091, commercially available fromSolvay; Carpol GP725, commercially available from Carpenter; PluracolTP740, commercially available from BASF; and Voranol 230-238, P425 andCastor Oil, commercially available from Dow Chemical Company.

The second polyol in the two-polyol blend has the followingcharacteristics: (a) the polyol has a functionality of three, preferablywith all of the hydroxyl groups being primary hydroxyls; (b) the polyolis a polyester or polyether polyol, preferably a polyether polyol; (c)the polyol has an OH index between approximately 800 and 1200 mgOH/g,preferably between approximately 900 and 1100 mgOH/g, and mostpreferably between approximately 935 and 1,050 mgOH/g; (d) the polyolhas a molecular weight between approximately 100 and 300, preferablybetween approximately 125 and 200, and most preferably betweenapproximately 150 and 190; and (e) the polyol has a viscosity belowapproximately 2,000 cps, preferably below approximately 1,500 cps. Tradenames of suitable polyols for use as the second polyol include Pluracol858, commercially available from BASF, and Multranol 9133, commerciallyavailable from Bayer MaterialScience.

The ratio of the first polyol to the second polyol is such that the OHindex of the blend is between approximately 350 and 700 mgOH/g,preferably between approximately 550 and 650 mgOH/g, and most preferablybetween approximately 575 and 625 mgOH/g.

According to another exemplary embodiment, the polyol component isprovided as a blend of three polyols.

The first polyol in the three-polyol blend is provided at a levelbetween approximately 20 and 50% of the blend, preferably betweenapproximately 25 and 35 percent, and most preferably approximately 30%,and has the following characteristics: (a) the polyol has afunctionality of three, preferably with all of the hydroxyl groups beingprimary hydroxyls; (b) the polyol is a polyester or polyether polyol,preferably a polyether polyol; (c) the polyol has an OH index betweenapproximately 200 and 300 mgOH/g, preferably between approximately 230and 250 mgOH/g, and most preferably between approximately 235 and 240mgOH/g; (d) the polyol has a molecular weight between approximately 600and 800, preferably between approximately 650 and 750, and mostpreferably between approximately 680 and 720; and (e) the polyol has aviscosity below approximately 500 cps, preferably below approximately400 cps, and most preferably between approximately 240 to 270 cps. Tradenames of suitable polyols for use as the first polyol include CAPA 3091,commercially available from Solvay; Carpol GP725, commercially availablefrom Carpenter; Pluracol TP740, commercially available from BASF; andVoranol 230-238, P425 and Castor Oil, commercially available from Dow.

The second polyol in the three-polyol blend is provided at a levelbetween approximately 20 and 40% of the blend, preferably betweenapproximately 25 and 35% and most preferably approximately 30%, and hasthe following characteristics: (a) the polyol has a functionality ofthree, preferably with all of the hydroxyl groups being primaryhydroxyls; (b) the polyol is a polyester or polyether polyol, preferablya polyether polyol; (c) the polyol has a OH index between approximately500 and 700 mgOH/g, preferably between approximately 600 and 700 mgOH/g,and most preferably between approximately 675 and 700 mgOH/g; (d) thepolyol has a molecular weight between approximately 200 and 300,preferably between approximately 225 and 275, and most preferablybetween approximately 240 and 250; and (e) the polyol has a viscositybelow approximately 1000 cps, preferably below approximately 900 cps.Trade names of suitable polyols for use as the second polyol includePluracol TP440, commercially available from BASF; Voranol 230-238,commercially available from Dow Chemical Company; and Multranol 9138,commercially available from Bayer MaterialScience.

The third polyol in the three-polyol blend is provided at a levelbetween approximately 20 and 50% of the blend, preferably betweenapproximately 30 and 45 percent, and most preferably approximately 40%,and having the following characteristics: (a) the polyol has afunctionality of three, preferably with all of the hydroxyl groups beingprimary hydroxyls; (b) the polyol is a polyester or polyether polyol,preferably a polyether polyol; (c) the polyol has an OH index betweenapproximately 800 and 1200 mgOH/g, preferably between approximately 900and 1100 mgOH/g, and most preferably between approximately 935 and 1050mgOH/g; (d) the polyol has a molecular weight between approximately 100and 300, preferably between approximately 125 and 200, and mostpreferably between approximately 150 and 190; and (e) the polyol has aviscosity below approximately 2,000 cps, preferably below approximately1,500 cps. Trade names of suitable polyols for use as the third polyolinclude Pluracol 858, commercially available from BASF and Multranol9133, commercially available from Bayer MaterialScience.

The percentages of the first, second and third polyols in thethree-polyol blend are such that the OH index of the blend is betweenapproximately 350 and 750 mgOH/g, preferably between approximately 625and 725 mgOH/g, and most preferably between approximately 650 and 700mgOH/g.

The polymeric additive, if included, performs only physical functionswithin the system. Depending on the system requirements, it may enhancemechanical or thermal properties or may improve the surface of the partby counteracting the common tendency of thermosetting polymers to shrinkslightly when they polymerize. According to an exemplary embodiment, thepolymeric additive performs only this shrink-reduction function, and maybe referred to as a “low-profile additive.” This function derives fromthe coefficient of thermal expansion of the additive, which causes it toincrease in volume at an appropriate time during the polymerization ofthe thermoset polymer system. Examples of acceptable low-profileadditives include polystyrene, styrene-acrylic copolymer, methacrylateresin, polyvinyl acetate, and capped PPO.

To prepare the resin, it is generally preferred that all of thecomponents except the isocyanate component are blended together inadvance of use. Because the isocyanate component is highly reactive, itis generally kept separate from the other components until just beforeuse. According to an exemplary embodiment, the isocyanate component isadded to the polyol-additive mixture less than five minutes before usein a pultrusion process. According to a particular exemplary embodiment,the isocyanate component is added to the polyol-additive mixture lessthan one minute before use. The isocyanate component and thepolyol-additive mixture are mixed together using a continuousmetering-mixing system according to an exemplary embodiment. Accordingto another exemplary embodiment, the isocyanate component is premixedwith one or more additives.

As the isocyanate component and the polyol-additive mixture enter acuring die of a pultrusion system, they may be in an immiscible liquidstate. According to a particular exemplary embodiment, the isocyanatecomponent and the polyol-additive mixture are immiscible, and the heatof the curing die accelerates the immiscible liquids toward solution.They then begin reacting. As the reaction progresses, the isocyanate andpolyol initially form a partially-reacted, highly-adhesive gelsubstance. This gel substance exists for a relatively short time,because of the nature of the isocyanate-polyol reaction. This reactionis an addition reaction; therefore, molecular weight builds slowly atfirst but becomes asymptotic and very high near completion. The resultis that the reactive mixture remains a liquid until the reaction is morethan 50 percent complete, then moves into the highly-adhesive gelledstate quickly and for only a very short time compared to other resinsystems employed in pultrusion.

In addition, a portion of the acid reacts with the calcium carbonatefiller, forming a metal soap, which also migrates to the metal surfaceof the die to enhance the lubricity of the metal surface. This reactionmay be supplemented by pre-treatment of the calcium carbonate prior tomixing of the system, which increases the stability of the system andincreases the amount of time the mixture can be stored without loss ofperformance.

As the isocyanate and polyol react, their density increases slightly(e.g., between approximately 0.5% and 1.0%), resulting in a commensuratedecrease in volume. Simultaneously, the temperature of the polymericadditive increases due to the heating of the die and the exothermic heatof reaction of the isocyanate and polyol, resulting in an increase inits volume.

The resin precursor systems disclosed herein have elastic moduli aftercuring of between approximately 350,000 and 500,000 psi, and preferablybetween 450,000 and 500,000 psi. In contrast to conventional resinsystems (e.g., unsaturated polyesters or epoxy vinyl esters), theelongation-to-failure of the resin systems disclosed herein after curingare between approximately 6% and 15% and preferably between 7.5% and10%. The increased elongation-to-failure of the resin systems allows forthe production of pultruded composite components in which the resincontinues to support reinforcing fibers under load and to cause the loadto be shared among a larger group of fibers as the applied load isincreased. Since the elongation-to-failure of the resin exceeds theelongation-to-failure of all commonly used fibers (including carbon,polymeric, and glass fibers) and the modulus of the resin system issufficient to distribute load effectively, it can be expected that thefailure mode of a pultruded structural shape under bending, compressive,tensile or torsional load will occur in the fibers (as opposed tooccurring in the resin). This can result in an increase in the ultimatestrength of a structure by a factor of two or three when compared to theultimate strength of the same component made with the same fiber contentbut with a conventional resin system such as polyester, vinyl ester orphenolic resins. In the case of these resins, it is common for thefailure mode to be the failure of the resin in shear, which results inthe buckling of unsupported fibers at loads far below the theoreticalload-carrying capacity of the fiber.

The ultimate strength advantage of the high-strength resin system alsoprovides benefits in the direction transverse to the primary load pathand orientation of the primary fiber reinforcement. Because of theultimate strength limits of the conventional resins, structures madewith them have very little transverse strength, unless reinforcingfibers with a transverse orientation are included. However, theinclusion of transverse fibers in a pultruded component adds both weightand cost to the structure. If a high-strength resin system issubstituted, the transverse strength is increased. In most cases, notransverse reinforcement is required at all.

An additional advantageous feature of utilizing such an improved resinsystem is that the structural characteristics of the pultruded componentare such that it can accept fasteners intended for drywall or sheetmetal without splitting, so that simple mechanical attachment methodscan be used in assembly and installation of the component. For example,fasteners such as screws, nails, or the like may be used to securepultruded lineals used in the production of windows and doors withoutthe risk of having the lineals split at the location of the fasteners.

The rheology and cure kinetics of the resin precursor system accordingto the exemplary embodiments described herein are such that it can berun at speeds comparable to or faster than conventional resin systems.The elimination of transverse reinforcing fibers may also provideimproved processing speeds for the production of the pultrudedcomponents. For example, while a conventional pultrusion process mayoperate at a speed of between approximately 3 and 5 feet per minute, apultrusion process that does not utilize transverse reinforcing fibersmay operate at a speed of between approximately 4 and 10 feet perminute.

Example 1

According to a theoretical exemplary embodiment, a resin precursorsystem is prepared that includes 169 parts by weight of an isocyanatecomponent, a two-component blend of polyols that includes 30.3 parts byweight of a first polyol component and 60.6 parts by weight of a secondpolyol component, 4.2 parts by weight of a mold release, and 4.2 partsby weight of a filler. The isocyanate component comprises BASF LupranateM20S, the first polyol comprises Carpenter Carpol GP725, the secondpolyol comprises Bayer Multranol 9133, the mold release comprisesTechnick Products CR-250, and the filler comprises Huber calciumcarbonate.

Example 2

According to another theoretical exemplary embodiment, a resin precursorsystem is prepared that includes 175 parts by weight of an isocyanatecomponent; a three-component blend of polyols that includes 27.5 partsby weight of a first polyol component, 27.5 parts by weight of a secondpolyol component, 36.6 parts by weight of a third polyol component; 4.2parts by weight of a mold release, and 4.2 parts by weight of a filler.The isocyanate component comprises Bayer Mondur 486, the first polyolcomprises Solvay CAPA 3091, the second polyol comprises Dow Voranol230-660, the third polyol comprises BASF Pluracol 858, the mold releasecomprises comprises Axel Plastics Pul-24, and the filler comprises Hubercoated calcium carbonate.

FIG. 3 is a schematic illustration of a system 100 for producing acomposite component using a pultrusion process according to an exemplaryembodiment. The manner in which the system 100 operates will bedescribed with reference to FIG. 7, which is a flow diagram illustratingsteps in the process or method 200 of producing composite componentsaccording to an exemplary embodiment.

Reinforcing materials in the form of fiber yarns or tows 110 areprovided on spools 122 that are arranged on a fixture such as a creel120. The spools 122 are arranged in a manner that allows each tow 110 tobe fed to the next step in the process without interference or tanglingwith other tows or with the creel 120. In the case of glass fiber towssupplied in 40 pound “doffs,” the doffs are arranged standing on end.The creel 120 acts to provide an array of doffs vertically andhorizontally such that the tows 110 are fed from the inside of the doff.In the case of carbon, polymeric, or other high-strength fibers, eachspool 122 is mounted on a spindle which may incorporate adjustableresistance to rotation. The spindles are arranged vertically andhorizontally so that they do not interfere or tangle.

Features (not shown) are provided for feeding each tow 110 through thecreel 120 to avoid interference. According to an exemplary embodiment,each tow passes through a series of holes in the creel structure. Theseholes may or may not be finished, or may incorporate inserts made of amaterial that reduces friction and prevents fraying of the fiber. Theholes are arranged within the structure in such a way that the fibers donot cross or contact each other. The tows are presented at the exit endof the creel in an array that makes the location of problems or missingtows obvious to the operator, and facilitates alignment of the tows asthey enter the next step in the process. According to an exemplaryembodiment, such features are of sufficient size to allow the passage offiber splices, which will be made when a spool of fiber runs out andneeds to be replaced without halting production.

In a step 210 (FIG. 7), each tow 110 is fed through an aperture or hole132 in a member or element shown as a supporting fixture 130 (e.g., aforming card). The supporting fixture 130 includes a plurality ofapertures 132 through which the tows 110 may be routed in a patternconsistent with the final design shape of the product to bemanufactured. According to an exemplary embodiment, the supportingfixture 130 is provided as a sheet of plastic (e.g., polyethylene,nylon, etc.) having a thickness of approximately 0.5 inches. Theapertures 132 have diameters of between approximately 0.25 and 0.5inches and are provided in an array with a distance between adjacentapertures of between approximately 0.5 and 1.0 inches. One function ofthe supporting fixture 130 is to provide the tows in a desired shapedirectly to a backing plate of an impregnation die without sagging orcrossing.

According to an exemplary embodiment, a system 140 is provided to meterand feed a high-strength, two-part polymeric resin precursor (e.g., athermosetting polyurethane-based resin precursor as described above)utilizing two containers 142 and 144 and a metering device 146. One ofthe containers (e.g., container 142) contains one of the reactivechemicals used to form the resin precursor and a variety of processingaids; the other container (e.g., container 144) contains a secondreactive chemical without any processing aids. The chemicals from thetwo containers are kept separate until just before they are to beintroduced into an impregnation die of a pultrusion system, when theyare simultaneously pumped and mixed a predetermined amount of timebefore they are to be introduced into the die.

It should be appreciated that the particular ratio of the constituentscontained in the containers 142 and 144 may vary depending on theparticular constituents utilized. The chemicals provided in each of thecontainers may vary according to other exemplary embodiments. Forexample, each of the containers may include both reactive chemicals andprocessing aids. According to still other exemplary embodiments, adifferent number of containers may be provided (e.g., three containersmay each contain a reactive chemical or two of the three containers mayinclude reactive chemicals and the third container may includeprocessing aids, pigments, UV stabilizers, etc.).

The components of the resin precursor are dispensed at the desired ratioby means of the metering device 146 (e.g., a metering pump system). Toprovide improved efficiency in the production of composite components,the chemicals in the two containers 142, 144 are provided in a mannerthat results in the full consumption of the reactive chemicals duringproduction of the composite components (i.e., the flow rate of thechemicals into an impregnation die matches the rate at which thechemicals are mixed). In this manner, the production of waste materialis reduced as compared to conventional pultrusion processes.

In the preferred embodiment, the pumping system provides for adjustmentof the ratio of the components, and runs at a speed that is matched tothe consumption of materials, and the components are mixed by means of adisposable static mixer 148. The mixing system may run at a continuousspeed matched to the rate of material consumption (i.e., the mixing ofchemicals may proceed at a rate that is substantially identical to therate of fluid flow into the impregnation die), or may operateintermittently to maintain a fluid level between minimum and maximumlevels in the subsequent step in the process.

According to an exemplary embodiment, the components are mixed less thanfive minutes before the resin precursor is provided to the first chamberof the impregnation die. According to another exemplary embodiment, thecomponents are mixed less than one minute before the resin precursor isprovided to the first chamber of the impregnation die. One advantage ofsuch a method is that the resin precursor is produced on demand duringthe production process, eliminating the need to store excess resinprecursor or to mix it beforehand.

The fiber tows 110 and mixed resin precursor 141 (FIG. 6) are eachintroduced into a device shown as an impregnation die 150 that isconfigured to coat individual filaments within each fiber tow thoroughlywith the resin, and to deliver an intimately-mixed resin-fiber mass withthe proper ratio of resin precursor and fiber in the proper geometry tothe entrance of a curing die. The device 150 includes a backing plate151 having a plurality of apertures or holes 153 provided therein and afirst chamber or zone 154 and a second chamber or zone 156 for wettingthe tows 110 with the resin system, as illustrated in FIGS. 4-6. Thetows 110 are first introduced into the first chamber 154 in a step 220(FIG. 7), followed by their introduction into the second chamber 156 ina step 230. The device 150 and the method of coating the fibers andyarns will be described in greater detail below.

Previously, the wetting of reinforcement materials was viewed as asingle step operation. To provide more complete wetting of the tows 110(and the individual fibers within the tows) as compared to conventionalpultrusion processes, the impregnation die 150 separates the process ofwetting the fiber into two distinct steps which are governed by the samephysical laws, but in different ranges and on different scales.

The process of wetting is so divided because the dynamics of the wettingprocesses are sufficiently different that different flow conditions mustbe maintained to maximize the efficiency of each step, and the flowconditions required for one step are not necessarily the same as orsimilar to the conditions required for the other. Both wetting steps aregoverned generally by two principles of physics. First, the flow offluids through porous media (e.g., wetting of the tows) is describedgenerally by Darcy's Law. Second, capillary action (e.g., wetting ofindividual filaments or fibers) is described generally by Washburn'sEquation.

Darcy's Law describes the flow of a liquid system through a porousmedium. Darcy's Law can be expressed in the equation

$Q = {{AK}\;\frac{\Delta\; h}{L}}$where Q is the volumetric flow rate, A is the flow area perpendicular toL, K is the hydraulic conductivity, and Δh/L is the change in hydraulichead over the path length. Although Darcy's Law can be said to takecapillary action into account via the K (hydraulic conductivity) term,in practical terms different values must be used as the scale changesand the relative importance of the forces involved changes, making itless effective at describing the entire wetting process.

Washburn's Equation describes the capillary flow of a fluid in a porousmedium, and takes into account the intermolecular forces between thefluid and the porous medium. It can be expressed in the followingequation:

$L^{2} = \frac{\gamma\;{Dt}}{4\eta}$where t is the time for a liquid of viscosity η and surface tension γ topenetrate a distance L into a fully wettable, porous material whoseaverage pore diameter is D.

The scale of the first-step process—the wetting of the exterior of thefiber tows—is in a range where Darcy's Law is dominant and capillaryaction has little if any influence. However, the scale of the secondstep process—the wetting of the individual filaments within each tow—isin a range where capillary action can become the most significant, oreven the dominant, wetting mechanism.

The first step in the wetting operation is the process of wetting theexterior of the fiber yarns or tows with the liquid resin precursor(e.g., step 220). The first chamber 154 is provided as a “bath” providedat atmospheric pressure, and the tows 110 enter the bath separated by asufficient distance to allow the liquid resin precursor 141 to flowfreely around the tows 110. To separate the tows 110 from each other,the tows enter the first chamber 154 through the backing plate 151,which includes an aperture 153 for each of the tows 110. The apertures153 are spaced from each other such that the distance between the towsis sufficient to allow the resin precursor 141 to flow through the massof fibers without impediment, and so that the resin precursor 141 isprovided in the first chamber without voids. The diameter of eachaperture 153 is larger than the diameter of the tows 110 to accommodaterelatively simple threading of the tows through the aperture and toallow the passage of splices when one spool of fiber runs out and isreplaced by another. The thickness of the plate is great compared to thetow diameter (in the range of 1 inch or greater). The resin precursor isprevented from running out of the first chamber 154 by the counter-flowmotion of the tows 110 through the apertures.

According to an exemplary embodiment, the bath is provided atatmospheric pressure. The liquid level in the bath is kept high enoughso that all fiber yarns or tows are covered with liquid for a sufficienttime to allow the resin precursor 141 to flow over and around all tows.As liquid exits the bath and enters the second chamber 156 (FIG. 4) withthe moving fiber mass, the level of the resin precursor 141 in the bathis maintained by adding resin precursor 141 into the first chamber 154from a continuous or intermittent pumping/metering/mixing system (e.g.,system 140).

Because the bath is provided at atmospheric pressure in first chamber154 and the tows 110 are separated from each other by an appropriatedistance, the exterior surfaces of the tows 110 are thoroughly wetted bythe force of gravity without impediment, so that the resin precursorfills the entire chamber without voids. After initial wetting, theresin-fibrous mass includes a significant excess of resin precursor(many times the amount of resin precursor that will eventually becomethe final part). The length of time required to wet the exterior of eachtow 110 is primarily dependent on the viscosity of the resin, but alsopossibly to a small degree by the interfacial surface tensionrelationship between the resin precursor and the fiber.

The second step of the process (e.g., step 230) is the penetration ofthe liquid resin precursor system into the interstitial spaces withinthe individual tows, among and around each fiber or filament. The wettedtows 110 enter the second chamber 156, which has a configuration that isintended to cause the liquid resin precursor to penetrate into theindividual tows 110 by creating the conditions necessary to cause theliquid resin precursor to penetrate into interstitial spaces between theindividual fibers in each tow 110.

According to an exemplary embodiment, the second chamber 156 includes atapered or decreasing cross-sectional area from its entrance to itsexit. The cross-sectional area and shape of the exit end of the secondchamber 156 is configured to approximate that of the entrance to thecuring die 160 and that of the final part. The degree of taper (theratio of entrance area to exit area) of the second chamber 156 may varybased on a variety of factors. Such factors may include, for example,the viscosity of the resin precursor system, the interfacial surfacetension of the resin precursor system with the fiber reinforcement, andthe start-up speed and targeted production speed of the product(s) beingmanufactured, among others.

While the individual tows have diameters of approximately one millimeteror less, the individual filaments or fibers are much smaller, havingdiameters of approximately 30 microns or less. At such a size, capillaryaction becomes a significant mechanism, even the dominant mechanism,influencing the speed and degree of wetting. Factors that may influencecapillary flow into the tow include the following:

-   -   1. The pore size (i.e., the size and shape of the passage into        the tow). Resin precursor flow into the interstitial spaces        inside a tow takes place laterally, perpendicular to the main        axis of the tow. The shape of the passage is rectangular, with        the dimension along the axis of the tow effectively infinite and        the dimension perpendicular to the fiber equal to the nominal        filament spacing within the tow.    -   2. The distance the resin precursor must travel. In the case of        the essentially cylindrical shape of a fiber tow, this distance        is equal to the radius of the fiber tow, since resin precursor        is flowing to the center of the tow from the entire perimeter.    -   3. The viscosity of the resin precursor system. Higher viscosity        decreases the speed of capillary action.    -   4. The interfacial surface tension between the resin precursor        system and the fiber. It is a measure of the attraction of the        resin precursor system to the fiber at an atomic level. Higher        interfacial surface tension indicates greater attraction of        resin precursor to fiber, and speeds capillary action.

If capillary action is slow due to low interfacial surface tension orhigh viscosity, the same Darcy's law factors that govern the wetting ofthe tow exteriors may be applied to model and influence wetting. In thatcase, the speed of flow is directly proportional to pressure, andpressure can be increased by constructing the impregnation die with asecond chamber tapered at a rate such that pressure build-up occurs. Thepressure buildup will be governed by the taper ratio, the viscosity ofthe resin precursor and the velocity of the fiber moving through thechamber.

According to an exemplary embodiment, the resin precursor 141 has aviscosity below approximately 2,000, and more desirably belowapproximately 1,000. The interfacial surface tension between the liquidand the fiber is greater than approximately 0.02 N/m and more desirablyabove 0.05 N/m. At these values, the first wetting step will requireless than approximately three seconds to complete, and the second stepwill require less than approximately ten seconds. At a tow velocity ofapproximately 60 inches per minute, the length of the first and secondchambers can be as short as approximately fifteen inches, and therequired taper of the second chamber needs only to be sufficient toreplace the air that escapes out of the tows through the entrance of thedevice.

In a step 240 (FIG. 7), the wetted, formed resin-fiber mass enters acuring die 160. Heat is applied to the resin-fiber mass by means of heatapplied to the curing die 160. The heating apparatus may be arranged soas to provide different amounts of heat and different temperaturesbetween the entrance and exit of the die, depending on the rheology ofthe resin precursor system used. According to an exemplary embodiment inwhich a polyurethane-based resin precursor is utilized, the curing die160 is heated to a temperature of between approximately 50 and 320degrees Celsius.

According to an exemplary embodiment, the curing die 160 is constructedof any suitable metal such as tool steel, aluminum, or another metal.The curing die 160 may be coated with a wear resistant coating to reduceerosion by the resin-fiber mass as it passes through the die. Theentrance of the curing die 160 may be configured such that there is anentrance taper, to provide added compression pressure to the resin-fibermass and insure impregnation of the resin. The exit of the curing die160 may be configured such that there is an exit taper to allow forthermal expansion, as required to minimize the friction and thereby thepulling force required.

According to an exemplary embodiment, the curing die 160 is heated withelectric resistance heaters in three heat zones arrayed above and belowthe die (not shown), with supplemental heating provided by individualresistance heaters applied externally to the sides of the die orinserted into chambers drilled into the die specifically for theinsertion of heaters. A cooling system (e.g., a chilled water system) isprovided at the entrance and exit of the die. The cooling system isintended to prevent premature curing of the resin precursor in thewetting device and to reduce the temperature of the part below its glasstransition temperature as it exits the die.

According to an exemplary embodiment, the resin-fiber mass travelsthrough the curing die at a speed of between approximately 1 and 20 feetper minute. The curing die has a length of between approximately 2 and 4feet according to an exemplary embodiment. It should be appreciated thatthe speed of travel of the resin-fiber mass, the length of the curingdie, and other parameters (e.g., temperature of the curing die, etc.)may vary according to other exemplary embodiments, and may depend on thetype of resin precursor system and reinforcement material utilized, thedesired rate of production, and the like.

Upon exiting the curing die 160, the cured part or product 112 isallowed to cool at room temperature in a step 250 (FIG. 7) to atemperature that allows handling of the part. According to an exemplaryembodiment, cooling of the product 112 is performed in a passive coolingprocess in which air circulates around the part over a distance ofapproximately 10 feet. According to other exemplary embodiments, thedistance through which the product travels in the cooling process maydiffer (e.g., the distance may be greater or less than 10 feet).According to still other exemplary embodiments, forced air or anothercooling system may be utilized to cool the part (e.g., a chilled waterbath, etc.).

The cured product 112 is extracted from the curing die 160 byapplication of a tensile force produced by a puller 170. The puller 170may be provided as a reciprocating gripping system or a continuouscaterpillar-like gripping system.

In a step 260 (FIG. 7), the cured product 112 is cut to specific lengthsusing a saw 180 or similar device. The saw is configured toautomatically cut the cured product 112 to specified lengths, and may becontrolled by a computing device or other mechanism. According to anexemplary embodiment, the saw is made of a material configured to formcuts in reinforced plastic components (e.g., a carbide or diamondabrasive material).

Those reviewing this disclosure will appreciate that the system andmethod for wetting the fibers and fiber tows may provide variousadvantages as compared to conventional wetting systems. For example, thesystem and method described according to the exemplary embodiments allowfor the production of fiber-reinforced plastic products in a high-speedcontinuous process, with sufficient strength, stiffness andenvironmental resistance to make them suitable for use as structuralmembers in architectural applications such as windows, doors andexterior fascia of commercial and residential construction.

It is important to note that the resin composition described in thevarious exemplary embodiments is illustrative only. Although only a fewembodiments of the present inventions have been described in detail inthis disclosure, those skilled in the art who review this disclosurewill readily appreciate that many modifications are possible withoutmaterially departing from the novel teachings and advantages of thesubject matter recited in the claims. Accordingly, all suchmodifications are intended to be included within the scope of thepresent invention as defined in the appended claims. The order orsequence of any process or method steps may be varied or re-sequencedaccording to alternative embodiments. Other substitutions,modifications, changes and omissions may be made in the design,operating conditions and arrangement of the exemplary embodimentswithout departing from the scope of the present inventions as expressedin the appended claims.

1. A resin precursor composition for use in the production of compositecomponents comprising: a mold release material; a filler material; anisocyanate component comprising a material selected from the groupconsisting of diphenylmethane diisocyanate, a polymeric isomer ofdiphenylmethane diisocyanate, and combinations thereof; and a blend ofthree polyether polyols, each of the polyols having a functionality ofthree in an amount such that the ratio of the isocyanate component tothe polyol blend is between approximately 80% and 115% ofstoichiometric, the polyether blend comprising: (a) betweenapproximately 20% and 50% of a first polyol having a molecular weight ofbetween approximately 600 and 800; (b) between approximately 20% and 40%of a second polyol having a molecular weight of between approximately200 and 300; and (c) between approximately 20% and 50% of a third polyolhaving a molecular weight of between approximately 100 and
 300. 2. Theresin precursor composition of claim 1, wherein the first polyol has anOH index of between approximately 200 and 300 mgOH/g, the second polyolhas an OH index of between approximately 500 and 700 mgOH/g, and thethird polyol has an OH index of between approximately 800 and 1200mgOH/g.
 3. The resin precursor composition of claim 1, wherein the firstpolyol has an OH index of between approximately 230 and 250 mgOH/g, thesecond polyol has an OH index of between approximately 600 and 700mgOH/g, and the third polyol has an OH index of between approximately900 and 1100 mgOH/g.
 4. The resin precursor composition of claim 1,wherein the first polyol has a viscosity of less than approximately 500cps, the second polyol has a viscosity of less than approximately 1000cps, and the third polyol has a viscosity of less than approximately2000 cps.
 5. The resin precursor composition of claim 1, wherein thefirst polyol has a viscosity of less than approximately 400 cps, thesecond polyol has a viscosity of less than approximately 900 cps, andthe third polyol has a viscosity of less than approximately 1500 cps. 6.The resin precursor composition of claim 1, wherein the first polyol hasa molecular weight of between approximately 650 and 750, the secondpolyol has a molecular weight of between approximately 225 and 275, andthe third polyol has a molecular weight of between approximately 125 and200.
 7. The resin precursor composition of claim 1, wherein thepolyether blend has an OH index between approximately 350 and 750mgOH/g.
 8. The resin precursor composition of claim 1, wherein thepolyether blend has an OH index between approximately 625 and 725mgOH/g.
 9. The resin precursor composition of claim 1, wherein the firstpolyol has an OH index between approximately 200 and 300 mgOH/g.
 10. Theresin precursor composition of claim 1, wherein the second polyol has anOH index between approximately 500 and 700 mgOH/g.
 11. The resinprecursor composition of claim 1, wherein the third polyol has an OHindex between approximately 800 and 1200 mgOH/g.
 12. The resin precursorcomposition of claim 1, wherein the first polyol has an OH index ofbetween approximately 200 and 300 mgOH/g and a viscosity of less thanapproximately 500 cps, the second polyol has an OH index of betweenapproximately 500 and 700 mgOH/g and a viscosity of less thanapproximately 1000 cps, and the third polyol has an OH index of betweenapproximately 800 and 1200 mgOH/g and a viscosity of less thanapproximately 2000 cps.
 13. The resin precursor composition of claim 1,wherein the blend comprises between approximately 25% and 35% of thefirst polyol, between approximately 25% and 35% of the second polyol,and between approximately 30% and 45% of the third polyol.
 14. The resinprecursor composition of claim 1, wherein the mold release material isprovided in an amount of between approximately 0.5% and 5% of the totalmass of the resin precursor composition.
 15. The resin precursorcomposition of claim 1, wherein the filler is provided in an amount ofbetween approximately 0.5% and 10% of the total mass of the resinprecursor composition.
 16. The resin precursor composition of claim 1,wherein the filler comprises at least one material selected from thegroup consisting of caolin clay, calcium carbonate, and combinationsthereof.
 17. The resin precursor composition of claim 1, wherein theresin precursor composition has an elongation-to-failure of betweenapproximately 6% and 15% after curing.
 18. The resin precursorcomposition of claim 1, wherein the resin precursor composition has anelastic modulus of between approximately 350,000 and 500,000 psi aftercuring.
 19. The resin precursor composition of claim 1, furthercomprising a polymeric additive configured to counteract shrinkage ofthe resin precursor composition during polymerization.
 20. Apolyurethane resin precursor composition for use in a pultrusion processcomprising: a mold release material; a filler material; an isocyanatematerial comprising a material selected from the group consisting ofdiphenylmethane diisocyanate, a polymeric isomer of diphenylmethanediisocyanate, and combinations thereof; and a polyol componentcomprising: (a) a first polyether polyol having a functionality of threeand a molecular weight of between approximately 600 and 800 and an OHindex of between approximately 200 and 300 mgOH/g; (b) a secondpolyether polyol having a functionality of three and a molecular weightof between approximately 200 and 300 and an OH index of betweenapproximately 500 and 700 mgOH/g; and (c) a third polyether polyolhaving a functionality of three and a molecular weight of betweenapproximately 100 and 300 and an OH index of between approximately 800and 1200 mgOH/g; wherein the polyol component comprises betweenapproximately 20% and 50% of the first polyether polyol, betweenapproximately 20 and 40% of the second polyether polyol, and betweenapproximately 20 and 50% of the third polyether polyol.
 21. The resinprecursor composition of claim 20, wherein the first polyether polyolhas an OH index of between approximately 230 and 250 mgOH/g, the secondpolyether polyol has an OH index of between approximately 600 and 700mgOH/g, and the third polyether polyol has an OH index of betweenapproximately 900 and 1100 mgOH/g.
 22. The resin precursor compositionof claim 20, wherein the first polyether polyol has a viscosity of lessthan approximately 500 cps, the second polyether polyol has a viscosityof less than approximately 1000 cps, and the third polyether polyol hasa viscosity of less than approximately 2000 cps.
 23. The resin precursorcomposition of claim 20, wherein the first polyether polyol has aviscosity of less than approximately 400 cps, the second polyetherpolyol has a viscosity of less than approximately 900 cps, and the thirdpolyether polyol has a viscosity of less than approximately 1500 cps.24. The polyurethane resin precursor composition of claim 20, whereinthe first polyether polyol has a viscosity below approximately 500 cpsand the third polyether polyol has a viscosity below approximately 2,000cps.
 25. The polyurethane resin precursor composition of claim 20,wherein the polyol component has an OH index of between approximately350 and 750 mgOH/g.
 26. The polyurethane resin precursor of claim 20,wherein the polyol component has an OH index of between approximately625 and 725 mgOH/g.
 27. The polyurethane resin precursor of claim 20,wherein the third polyether polyol has a viscosity of belowapproximately 1,500 cps.
 28. The polyurethane resin precursorcomposition of claim 20, wherein the filler comprises at least onematerial selected from the group consisting of caolin clay, calciumcarbonate, and combinations thereof.
 29. The polyurethane resinprecursor composition of claim 20, further comprising a polymericadditive configured to counteract shrinkage of the resin precursorcomposition during polymerization.
 30. The polyurethane resin precursorcomposition of claim 20, wherein the resin precursor composition has anelongation-to-failure of between approximately 6% and 15% after curing.31. The polyurethane resin precursor composition of claim 20, whereinthe resin precursor composition has an elastic modulus of betweenapproximately 350,000 and 500,000 psi after curing.
 32. A method forproducing a resin precursor composition comprising: mixing a polyolblend with a mold release material and a filler material to form a firstresin precursor component, the polyol blend comprising betweenapproximately 20% and 50% of a first polyol having a molecular weight ofbetween approximately 600 and 800, between approximately 20% and 40% ofa second polyol having a molecular weight of between approximately 200and 300, and between approximately 20% and 50% of a third polyol havinga molecular weight of between approximately 100 and 300; mixing a secondcomponent with the first component to form a resin precursorcomposition, the second component comprising an isocyanate comprising amaterial selected from the group consisting of diphenylmethanediisocyanate, a polymeric isomer of diphenylmethane diisocyanate, andcombinations thereof; wherein the step of mixing the second componentwith the first component is performed less than approximately fiveminutes before the resin precursor composition is to be provided to animpregnation die of a pultrusion process.
 33. The method of claim 32,wherein the step of mixing the second component with the first componentis performed at a rate that matches the rate of consumption of the resinprecursor composition in a pultrusion process.
 34. The method of claim32, further comprising curing the resin precursor composition such thatit has an elastic modulus of between approximately 350,000 and 500,000psi and an elongation-to-failure of between approximately 6% and 15%.35. The method of claim 32, wherein the polyol blend comprises betweenapproximately 25% and 35% of the first polyol, between approximately 25%and 35% of the second polyol, and between approximately 30% and 45% ofthe third polyol.
 36. The method of claim 32, wherein the first polyolhas an OH index of between approximately 200 and 300 mgOH/g, the secondpolyol has an OH index of between approximately 500 and 700 mgOH/g, andthe third polyol has an OH index of between approximately 800 and 1200mgOH/g.
 37. The method of claim 32, wherein the first polyol has an OHindex of between approximately 230 and 250 mgOH/g, the second polyol hasan OH index of between approximately 600 and 700 mgOH/g, and the thirdpolyol has an OH index of between approximately 900 and 1100 mgOH/g. 38.The method of claim 32, wherein the first polyol has a viscosity of lessthan approximately 500 cps, the second polyol has a viscosity of lessthan approximately 1000 cps, and the third polyol has a viscosity ofless than approximately 2000 cps.
 39. The resin precursor composition ofclaim 32, wherein the first polyol has a viscosity of less thanapproximately 400 cps, the second polyol has a viscosity of less thanapproximately 900 cps, and the third polyol has a viscosity of less thanapproximately 1500 cps.
 40. The resin precursor composition of claim 32,wherein the first polyol has a molecular weight of between approximately650 and 750, the second polyol has a molecular weight of betweenapproximately 225 and 275, and the third polyol has a molecular weightof between approximately 125 and
 200. 41. The method of claim 32,further comprising providing the resin precursor composition into animpregnation die of a pultrusion process.
 42. The method of claim 41,wherein the mold release material comprises an acid that is attracted towalls of the impregnation die.
 43. The method of claim 41, wherein aportion of the mold release material reacts with the filler material toform a metal soap.